<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;

        }
        .wrap{
            width: 100%;
            height: 500px;
            background: orange
            ;
            margin-top: 100px;
        }
        .container{
            height: 200px;
            background: green
            ;
            opacity: 0.5;
            margin-top: 100px;
        }
        .box{
            height: 100px;
            background: pink;
            margin-top: 50px;
        }
        .BFC{
            position: absolute;
            display: block;
            width: 100%;
        }
    </style>
</head>
<body>
    <div class="wrap BFC">
        <div class="container">
            <div class="box">

            </div>
        </div>
    </div>
</body>
</html>